Devices of that type are already known, in particular the mechanism described by U.S. Pat. No. 4 681 993 which includes a spring whose rod is hinged on a fork-shaped link, secured to a shaft which, depending on the embodiment, can be different from the respective shafts of a disk for tensioning the spring and of a drive disk. In one of the embodiments, the tensioning disk and the drive disk are mounted on a common shaft which therefore requires two bearings to be provided in the housing.
The drawback of that mechanism is due in particular to the fact that the working angle, i.e. the angle through which the link is coupled to the rod of the spring is much less than 180.degree..
Another device of that type is described in publication DE-U-1 962 091 in which the mechanism has locking means at its dead points which are offset relative to one another by a pivot angle of 180.degree.. It also has a hook-shaped coupling bar.